Current world status of Balantidium coli

Abstract

Balantidium coli is a cosmopolitan parasitic-opportunistic pathogen that can be found throughout the world. Pigs are its reservoir hosts, and humans become infected through direct or indirect contact with pigs. In rural areas and in some developing countries where pig and human fecal matter contaminates the water supply, there is a greater likelihood that balantidiosis may develop in humans. The infection may be subclinical in humans, as it mostly is in pigs, or may develop as a fulminant infection with bloody and mucus-containing diarrhea; this can lead to perforation of the colon. The disease responds to treatment with tetracycline or metronidazole. Balantidiosis is a disease that need never exist given access to clean water and a public health infrastructure that monitors the water supply and tracks infections. Its spread can be limited by sanitary measures and personal hygiene, but it is a disease that will be around as long as there are pigs. Immunocompromised individuals have developed balantidiosis without any direct contact with pigs, perhaps with rats or contaminated produce as a possible source of infection. For the clinician, balanatidiosis should be included in the differential diagnosis for persistent diarrhea in travelers to or from Southeast Asia, the Western Pacific islands, rural South America, or communities where close contact with domestic swine occurs. Warming of the earth's surface may provide a more favorable environment, even in the now-temperate areas of the world, for survival of trophic and cystic stages of Balantidium, and its prevalence may increase. Effective sanitation and uncontaminated water are the most useful weapons against infection. Fortunately, balantidiosis responds to antimicrobial therapy, and there have been no reports of resistance to the drugs of choice.

FIG. 1.

Life cycle of Balantidium infection in humans. The trophozoites and cysts are shed in feces (1), and if the cysts, in particular, contaminate drinking water or food, the infection can be spread to other humans (2). Fruits and vegetables may also be contaminated by cysts and serve as a means of transmission. The bottom panel illustrates the pattern of encystment and asexual reproduction in trophic ciliates. (Reprinted from the CDC-DPDx Parasite Image Library [http://www.dpd.cdc.gov/dpdx/].)

FIG. 2.

Trophic stage of Balantidium. The surface of the organism is uniformly covered by cilia, and the lighter areas in the cytoplasm represent a contractile vacuole (CV) and the macronucleus (Mn). The oral apparatus (OA) is at the apical end of the organism in this micrograph. (Reprinted from the CDC-DPDx Parasite Image Library [http://www.dpd.cdc.gov/dpdx/].)

FIG. 3.

View of intestinal lumen with two trophic ciliates. The prominent macronucleus is seen in this stained section. The upper ciliate shows the small micronucleus nestled against the macronucleus. (Reprinted from the CDC-DPDx Parasite Image Library [http://www.dpd.cdc.gov/dpdx/].)

FIG. 4.

Encysted ciliate. The cytoplasm is protected from environmental stress within a double-walled covering. (Reprinted from the CDC-DPDx Parasite Image Library [http://www.dpd.cdc.gov/dpdx/].)